Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $208.71   9.129%   $227.7631   $227.76   $227.75   $227.80  
  Purchase #2 $100.51   3.264%   $103.7906   $103.79   $103.80   $103.80  
  Purchase #3 $211.92   3.791%   $219.9539   $219.95   $219.95   $220.00  
  Purchase #4 $182.87   3.569%   $189.3966   $189.40   $189.40   $189.40  
  Purchase #5 $35.39   9.528%   $38.762   $38.76   $38.75   $38.80  
  Purchase #6 $118.77   11.737%   $132.71   $132.71   $132.70   $132.70  
  Purchase #7 $105.81   7.724%   $113.9828   $113.98   $114.00   $114.00  
  7 purchase totals = $963.98       $1,026.3590   $1,026.35   $1,026.35   $1,026.50